Calibration of impedance monitoring of respiratory volumes using thoracic D.C. impedance

Abstract

A system includes an implantable medical device that includes a trans-thoracic impedance measurement circuit providing a trans-thoracic impedance signal of a subject. A controller is coupled to the trans-thoracic impedance circuit. The controller extracts a respiration signal from the trans-thoracic impedance signal, measures a breathing volume of the subject using the amplitude of the respiration signal and a breathing volume calibration factor, computes an adjusted breathing volume calibration factor using a reference baseline value of the trans-thoracic impedance and a measured baseline value of the trans-thoracic impedance, and computes a calibrated breathing volume using the adjusted breathing volume calibration factor.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is related to co-pending, commonly assigned U.S. patent application Ser. No. 10 / 921,503, entitled “THORACIC IMPEDANCE DETECTION WITH BLOOD RESISTIVITY COMPENSATION,” filed on Aug. 19, 2004 and is incorporated herein by reference.TECHNICAL FIELD [0002] The field generally relates to implantable medical devices and, in particular, but not by way of limitation, to systems and methods for monitoring respiratory volumes using electrical measurements of trans-thoracic impedance. BACKGROUND [0003] Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac rhythm management (CRM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), and devices that include a combination of pacing and defibrillation. The devices are typically used to treat patients using electrical therapy and to aid a physician or caregiver in patient d...

AI Technical Summary

Benefits of technology

[0005] The present inventors have recognized a need for improved monitoring of lung tidal volumes, or breathing volumes, using medical devices. This document discusses, among other things, systems and methods for monitoring lung tidal volume. A system embodiment comprises an implantable medical device that includes a trans-thoracic impedance measurement circuit. The trans-thoracic impedance measurement circuit provides a trans-thoracic impedance signal of a subject. A controller is coupled to the trans-thoracic impedance circuit. The controller extracts a respiration signal from the trans-thoracic impedance signal, measures a breathing volume of the subject using the amplitude of the respiration signal and a breathing volume calibration factor, computes an adjusted breathing volume calibration factor, and computes a calibrated breathing volume using the adjusted breathing volume calibration factor. The adjusted breathing volume calibration factor is computed using a reference baseline value of the trans-thoracic impedance and a measured change from the reference baseline value of the trans-thoracic impedance.

Problems solved by technology

This results in an inadequate amount of blood being pumped into circulation.

The reduced ability to move blood from veins to arteries may increase volume and pressure within the heart leading to heart failure progression.

If left unchecked, CHF can lead to death.

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